1. Field of the Invention
This invention relates to a cylindrical roller bearing.
2. Description of the Related Art
A roller chain is disclosed in Japanese utility Model Laid-Open Publication No. SHO-62-44579, wherein two inner plates and two outer plates disposed on both outer sides of the inner plates are connected together by a pin with a roller interposed therebetween the inner plates. The roller and the pin define therebetween an annular space in which a plurality of cylindrical rollers are disposed for rotation without using a retainer. A pair of annular side plates for controlling the positions of the plurality of cylindrical rollers in an axial direction are disposed at opposite end portions of an inner circumferential surface of the roller.
In the disclosed roller chain, the roller acts as an outer race of a cylindrical roller bearing, the plurality cylindrical rollers act as rolling members of the cylindrical roller bearing, and the pin acts as an inner race of the cylindrical roller bearing. Accordingly, the roller, the plurality of cylindrical rollers and the pin cooperatively form a so-called xe2x80x9copen-typexe2x80x9d cylindrical roller bearing which is devoid of a retainer for retaining or holding the cylindrical rollers within an annular space defined between the inner and outer races.
Japanese Patent Laid-Open Publication No. HEI-9-49528 and its related U.S. Pat. No. 5,823,686 discloses a chain for a conveyor in which a cylindrical roller bearing is incorporated. In the disclosed conveyor chain, a pair of inner plates are connected to each other by a bush, and a pair of outer plates are positioned in an overlapping relationship on the opposite outer sides of the pair of inner plates. The inner plates and the outer plates are articulately connected to each other by a pin extending through the bush. A plurality of cylindrical rollers made of steel and a plurality of cylindrical rollers made of resin are disposed alternately as rolling members on an outer periphery of the bush without using a retainer. A roller made of steel and having a pair of annular flanges extending from the opposite axial ends thereof in a radial inward direction is fitted for rotation on an outer periphery of the plurality of cylindrical rollers. Axial end faces of the cylindrical rollers of steel and resin are opposed to the inside surfaces of the annular flanges. Further, a pair of annular side plates are fitted on the outer periphery of the bush between the opposing inner faces of the pair of inner plates and the outer side faces of the roller. The pair of annular side plates control the position of the roller in its axial direction.
In the disclosed conveyor chain, the roller acts as an outer race of a cylindrical roller bearing, the cylindrical rollers made of steel and resin (polyethylene resin) act as rolling members of the cylindrical roller bearing, and the bush acts as an inner race of the cylindrical roller bearing. Accordingly, the roller, the cylindrical rollers made of steel and polyethylene resin, and the bush cooperatively form an unlubricated cylindrical roller bearing which is devoid of a retainer for holding the cylindrical rollers. Further, in the conveyor chain, since rotation of the roller is performed smoothly without being lubricated due to a self-lubrication property of the cylindrical rollers made of polyethylene resin, no maintenance is required. Consequently, the chain is particularly useful when embodied in a chain for conveyors designed for use in a field of food processing industry or the like wherein lubricating oil cannot be used.
However, in the roller chain disclosed in Japanese Utility Model Laid-Open Publication No. SHO-62-44579, when an axial load is applied to the roller (namely, the outer race of the cylindrical roller bearing), then a skew, that is, inclination of a cylindrical roller with respect to its normal axis of rotation, occurs with a plurality of cylindrical rollers (namely, the rolling members of the cylindrical roller bearing). When the roller rotates in this state, then a plurality of cylindrical rollers are displaced in an axial direction until end faces of the plurality of cylindrical rollers are contacted with, and slidably move on, one of the annular side plates. Thus, the roller chain is disadvantageous in that, by the sliding movement, abrasion occurs with the end faces of the plurality of cylindrical rollers and the annular side plates and this hinders smooth rotation of the roller.
Meanwhile, in the chain for a conveyor disclosed in Japanese Patent Laid-Open Publication No. HEI-9-49528, when the roller (outer race) is formed as a roller devoid of inwardly extending flanges for controlling the axial positions of the cylindrical rollers and the end faces of the cylindrical rollers of steel and resin (rolling members) are opposed to the annular side plates, an axial load applied to the roller would cause a skew of the cylindrical rollers of steel and resin in the same manner as the roller chain disclosed in Japanese Utility Model Laid-Open Publication No. SHO-52-44579 discussed above. When the roller rotates in this state, then a plurality of cylindrical rollers of steel and resin are displaced in an axial direction until the end faces of these cylindrical rollers are contacted with and slidably move on one of the annular side plates. By the sliding movement, abrasion occurs with the end faces of the plurality of cylindrical rollers of steel and resin and the annular side plates similarly, and this sometimes makes it difficult to use the chain for a long time without lubrication.
It is an object of the present invention to provide a cylindrical roller bearing wherein rotation of an outer race is stable against an axial load applied to the outer race and abrasion of an end face of a cylindrical roller and a thrust bearing plate can be suppressed.
In order to attain the object described above, according to the present invention, there is provided a cylindrical roller bearing, comprising: a plurality of cylindrical rollers; a circular outer race devoid of an annular flange extending from each of opposite axial ends of the outer race in a radial inward direction for controlling the position of the cylindrical rollers in an axial direction; and a circular inner race devoide of an annular flange extending from each of opposite axial ends of the inner race in a radial outward direction for controlling the position of the cylindrical rollers in the axial direction, the cylindrical rollers being disposed between the outer race and the inner race without using a retainer. A pair of thrust bearing plates are disposed on the opposite sides of the outer race for controlling the positions of the outer race and the cylindrical rollers in the axial direction. At least one of the cylindrical rollers is formed shorter than the other cylindrical rollers.
In the cylindrical roller bearing, when an axial load is applied to the outer race, a skew (i.e., inclination of a cylindrical roller with respect to its normal axis of rotation) occurs with some of the cylindrical rollers. However, the skew is taken up or canceled out by circumferential gaps formed between the shorter cylindrical roller and adjacent ones of the other cylindrical rollers at opposite longitudinal ends of the shorter cylindrical roller. Thus, the skew is not transmitted to the remaining ones of the cylindrical rollers. As a result, even when the outer race of the cylindrical roller bearing rotates in this state, the rotation of the outer race is stable, and the end faces of the remaining cylindrical rollers are not brought into contact with the thrust bearing plates. Accordingly, abrasion of the end faces of the cylindrical rollers and the annular thrust bearing plates by sliding movement between them can be suppressed.
Further, when the outer race of the cylindrical roller bearing is subjected to an axial load tending to displace the outer race in an axial direction, the position of the outer race in the axial direction is controlled by the thrust bearing plates.
Thus, with the cylindrical roller bearing, the following advantages are achieved.
First, when an axial load is applied to the outer race of the cylindrical roller bearing while the outer race is rotating, a possible skew is taken up or canceled out by the circumferential gaps formed between the cylindrical roller or rollers having the smaller length and adjacent ones of the resin cylindrical rollers. Accordingly, the rotation of the outer race is stable, and abrasion of the end faces of the cylindrical rollers and the thrust bearing plates by sliding contact between them can be suppressed.
Second, when the outer race of the cylindrical roller bearing is subjected to an axial load, the axial position of the outer race is controlled by the thrust bearing plates.
Third, even when an axial load is applied to the outer race of the cylindrical roller bearing, since a possible skew is taken up or canceled out by the circumferential gaps formed between the shorter cylindrical roller or rollers and adjacent ones of the cylindrical rollers, abrasion of the end faces of the cylindrical rollers and the thrust bearing plates by sliding contact between them can be suppressed. Accordingly, in the case of the roller bearing including steel cylindrical rollers and resin cylindrical rollers arranged alternately as the rolling members, such a cylindrical roller bearing can be used without lubrication for a longer period of time than the conventional unlubricated cylindrical roller bearing described hereinabove.